Also Known As
MG
This article was last reviewed on
This article waslast modified on
October 10, 2017.
What is myasthenia gravis?

Myasthenia gravis (MG) is a chronic autoimmune disease that affects skeletal muscle strength by impeding the communication between nerves and muscles. MG is typically first noticed when it causes weakness in eye muscles and symptoms such as a drooping eyelid and/or double vision. This is often referred to as ocular MG. From the eye muscles, it can spread over time to facial and neck muscles, causing weakness, slurred speech, difficulty chewing and swallowing, and/or difficulty breathing, and from the head and neck to other parts of the body, resulting in generalized MG. Muscle weakness will vary over time; it tends to worsen with sustained effort and improves with rest.

Body movements, including those as small as keeping the head upright and eyes open, are normally carried out by a coordinated series of muscle contractions. These muscle contractions are initiated by chemical nerve signals. On a microscopic level, a nerve impulse travels to a nerve ending and acetylcholine, a neurotransmitter, is released. This chemical travels from the nerve ending to a muscle fiber across a tiny gap that exists at the "neuromuscular junction" and it binds to one of many acetylcholine receptors on the muscle fiber. This binding activates the receptor and initiates muscle contraction.

With MG, the body's immune system produces proteins (autoantibodies) that target a person's own acetylcholine receptors and block or destroy them (acetylcholine receptor antibodies). This inhibits the receipt of acetylcholine signals and causes weakness and rapid muscle fatigue.

In the United States, MG is estimated to affect about 5 to 20 people in 100,000. Anyone can develop MG, but it is most frequently diagnosed in men over 60 years of age and in adult women younger than 40. During pregnancy, a woman with MG may pass acetylcholine receptor antibodies to her fetus. This can cause a newborn to have symptoms of MG, but the symptoms typically resolve within 2-3 months of birth.

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About Myasthenia Gravis
  • Causes

    The cause of MG is not known, but about 75% of those affected have an abnormally large thymus gland and some develop thymomas (generally benign tumors of the thymus). The thymus is a small gland located behind the upper breastbone. It plays an active role in the immune system through young adulthood, but normally begins to shrink after puberty and is less active in adults. The relationship between MG and the thymus is not fully understood, but some think that the thymus plays an indirect role in triggering acetylcholine receptor antibody production.

    Those who have MG are at an increased risk of also developing other autoimmune disorders, such as lupus, rheumatoid arthritis, or Graves disease.

    A small percentage of those with MG have an affected family member, but most do not. Congenital myasthenic syndrome is an inherited condition that causes symptoms similar to MG, but it is not an autoimmune disorder. Another condition, Lambert-Eaton Myasthenic Syndrome, can also cause similar symptoms, but it involves interference with the release of acetylcholine by the nerve ending, not acetylcholine receptor activity.

  • Signs and Symptoms

    A person with myasthenia gravis (MG) may experience a variety of symptoms. These may vary from day to day, worsen after activity and later in the day, and improve with rest. Symptoms may stay confined to the muscles around the eyes (ocular MG), but in most people they will extend to the face, neck, and other parts of the body within about a year (generalized MG). MG symptoms tend to worsen for several years and then stabilize. Some people may go through extended periods of remission.

    Symptoms may include:

    • Drooping eyelid
    • Double vision
    • Decreased eye movement control
    • Difficulty swallowing, chewing, with choking, drooling and gagging
    • Slurred speech
    • Weak neck muscles
    • Trouble holding up head
    • Difficulty breathing
    • Difficulty walking and an altered gait
    • Specific muscle weakness but normal feelings/sensations


    When MG affects the muscles that control breathing, it can cause a medical emergency called a myasthenic crisis that often requires hospitalization and may require the temporary use of a respirator to assist ventilation.

    Heat, stress, illness, and certain medications can cause symptoms to worsen.

  • Tests

    The goals with testing are to diagnose myasthenia gravis (MG), distinguish it from other conditions with similar symptoms, and to guide treatment. Some tests may be performed to monitor a person's health status over time.

    Laboratory tests
    Laboratory testing may include the measurement of one or more autoantibodies:

    • Acetylcholine receptor (AChR) antibodies—found in up to 90% of those with generalized MG and about 50% of those with ocular MG; this is the primary blood test for MG. There are three types of AChR antibodies: binding (most frequently tested), blocking, and modulating.
    • Anti-MuSK (muscle-specific kinase) antibodies—found in about 50% to 70% of those who are negative for AChR antibodies and have generalized MG.
    • Anti-striated muscle antibodies—found in about 80% of those with MG who have an enlarged thymus gland and indicate a significantly increased likelihood of the person having a thymoma (generally benign tumor of the thymus).


    Other testing that may sometimes be ordered:


    Non-laboratory tests

    One or more of these evaluations may be done to aid diagnosis, especially if laboratory testing was inconclusive:

    • Tensilon test (acetylcholinesterase test using edrophonium)—a person is given a drug intravenously to see if muscle strength improves for a few minutes (for more on this, see MedlinePlus Medical Encyclopedia: Tensilon test).
    • Repetitive nerve stimulation and/or single-fiber electromyography—to evaluate neuromuscular response in a specific area.
    • A chest CT (computed tomography)—to detect an enlarged thymus gland or thymoma.
    • A brain and eye orbit MRI (magnetic resonance imaging)—this is not routine but can help rule out other causes of eye-related symptoms.
  • Treatment

    There is no way to prevent or cure myasthenia gravis (MG), but its symptoms can be managed and most of those affected can lead normal or near-normal lives. The most significant complication, a myasthenic crisis that affects a person's ability to breathe, must be treated as a medical emergency and frequently requires hospitalization.

    Management of MG may include:

    • Acetylcholine esterase (AChE) inhibitors/Cholinesterase inhibitors—drugs that improve nerve and muscle communication and improve muscle strength by increasing the amount of acetylcholine at the neuromuscular junction; primary treatment for MG.
    • Thymectomy— the surgical removal of the thymus gland; may be performed when a thymoma (generally benign tumor of the thymus) is present. This can reduce symptoms and, in some cases, may resolve them.

    Other types of treatments are available to manage MG, to suppress the immune response and/or remove or block autoantibodies in the blood. For additional details on these, visit the Treatment for MG page on the Myasthenia Gravis Foundation of America web site.

    Newborns that acquire MG symptoms from their mothers must be closely monitored for a couple of weeks until the influence of the mothers' antibodies subsides.

    A person's treatment needs will vary over time. Those affected should work closely with their healthcare provider to determine the treatments appropriate for their changing health status.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used. To access online sources, copy and paste the URL into your browser.

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